In the examples we saw before, eye-tracking is just a technique we could use to do the same kind of research as what we do with self-paced reading; the only difference is that eye-tracking will give us more detailed and fine-grained measurements, and will allow participants to read the sentences more naturally. But the kind of research we would use eye-tracking for might not look fundamentally different from the kind of research we would use self-paced reading for.
Those were just a few examples, though. There are other situations where we can use eye-tracking to do totally different research which would not be possible with self-paced reading.
One example is research using the gaze-contingent boundary paradigm (sometimes just called the "boundary paradigm" for short). To learn about this, view the attached slides. The slides contain animations, so I recommend you view them in full-screen mode and move through them by clicking "Enter" or the arrow keys on your keyboard.
After viewing the slides, answer the following question: Do the results of the experiment by Yan and colleagues (2011) suggest that people can partially understand the meaning of words they see out of the corner of their eye, or do the results suggest that people cannot do this?
And if you're interested in learning more about eye-tracking research on reading, here's a useful bibliography of review and summary papers:
by Stephen Politzer-Ahles. Last modified on 2021-05-14. CC-BY-4.0.